This invention relates to wireless communication systems and, more particularly, to a wireless communication system used as a security system.
In some types of security systems it is desired to allow a mobile unit to be able to move throughout a predetermined area in safety. Such systems would generate an alert of some type when the mobile unit moves out of the predetermined area. The mobile unit can be any inanimate object, such as a motor vehicle or a container capable of being transported, or the mobile unit can be any living being, such as a pet or a human.
Some security systems utilize a centralized radio transmitter with a radio receiver located on the mobile unit. When the mobile unit strays out of range of the transmitter, the radio receiver assumes the mobile unit has strayed out of the predetermined area and provides some sort of feedback to the mobile unit. Additionally, other systems have been developed (see U.S. Pat. Nos. 5,852,403 and 5,872,516) to track the movements of pets and provide feedback if the pet strays from a predetermined area. One such system utilizes a radio transmitter that sends a radio signal to a radio receiver located on the pet. The radio receiver senses phase differences to determine if the pet has strayed out of the predetermined area. Another such system provides for a multiplicity of ultrasonic radio transmitters, stationed around the periphery of the predetermined area, which transmit to an ultrasonic receiver located on the pet. Based on the presence or absence of the received ultrasonic signal, the receiver determines if the pet has strayed from the predetermined area and provides some sort of feedback to the pet. Other pet security systems on the market today utilize lengths of wire strung underground, the length of wire mark the periphery of the predetermined area. A radio receiver located on the pet can sense the presence of the underground wire and, in a similar manner to the above, provide some sort of feedback if the pet has strayed from the predetermined area.
There are various problems with each of the above systems. Systems involving lengths of wire buried underground are expensive to install and repair. These systems are also difficult to install if a solid obstruction, for example a driveway, is in the way. Furthermore, various xe2x80x9caccidentsxe2x80x9d can cut the wires, thus rendering the system non-functional. Additionally, the system could be extremely difficult to repair since it may not be evident at what specific location the wires are broken.
Systems that assume that the pet has left the predetermined area when no longer in communication with the radio transmitter also have deficiencies. First, the predetermined area may be of limited size depending upon the maximum transmit power of the central radio transmitter allowed under local or federal law. Second, radio systems are notorious for being susceptible to variations in the received signal strength of a radio signal from well-known phenomena such as shadow fading, multipath fading, etc. Therefore, simply because the pet""s radio receiver does not receive radio messages for a period of time does not mean that the pet has strayed from the predetermined area. Third, such a system does not easily allow for an irregularly shaped predetermined area. For example, if the predetermined area has a swimming pool in the middle, the pet owner may wish to allow the pet access to the entire area with the exception of the pool area. A system that utilizes a radio transmitter that sends a radio signal to a radio receiver located on the pet could not cover this circumstance.
The system utilizing a multiplicity of ultrasonic radio transmitters transmitting to an ultrasonic receiver located on the pet is somewhat better in design, as it could to some degree handle irregularly shaped predetermined areas. However, the presence of an ultrasonic transmitter is costly both from the standpoint of electrical power and the cost of each such transmitter. Furthermore, the orientation of the receiver, such as whether the receiver was in a line of sight orientation with the ultrasonic transmitter or was shielded by the body of the pet, would tend to make the specific dividing line between the predetermined area and unsafe areas fuzzy and non-specific. The propagation characteristics of such a transmitter are such that the incident energy decreases as the square of the distance; a communications technology in which the incident energy decreased more rapidly than the square of the distance would tend to create a more clearly defined dividing line. Thus, a fully deployed system utilizing the ultrasonic technology for an extremely irregularly shaped predetermined area could be costly, the dividing lines could be difficult to predict, and such a system may also be difficult to maintain due to the cost and/or complexity of equipment involved in such a system. For example the cost of battery replacement in such a system can be very costly.
Therefore, the objective of this invention is to develop a system that does not suffer from the problems mentioned above. Specifically, a system is needed that can handle predetermined areas of arbitrary geometry with relatively clearly defined dividing lines without drastically increasing the cost or the complexity of installation or maintenance.
The invention solves the above and other problems by providing a system that includes a mobile transmitter and a plurality of boundary tags for receiving communication from the mobile transmitter. The mobile transmitter can be part of a mobile transceiver that also includes a mobile receiver. Preferably the mobile transmitter is coupled to a mobile unit, which can be an inanimate object capable of moving or being moved, or it can be coupled to a living being. The placement of the boundary tags mark the boundaries of a predetermined area, i.e., the area within which the mobile unit is allowed to move.
The mobile transmitter transmits a signal to at least one boundary tag. The system determines if the mobile transmitter has come into proximity of the at least one boundary tag by receiving a reflected modulated signal from the at least one boundary tag. If the mobile transmitter has come into proximity of a boundary tag a response is generated. The response can be a stimulus or an alert, or both. The response can be generated at the transceiver, or at a central control station.
In one embodiment of the invention, the at least one boundary tag modulates a reflection of the signal transmitted by the mobile transmitter. This reflected modulated signal is received by the mobile transmitter. When the mobile receiver receives the reflected modulated signal, it can either: determine if the mobile transmitter has come into the proximity of a boundary tag; or it can forward information obtained from the signal to a central control station that would determine if the mobile transmitter has come into the proximity of a boundary tag.
In an alternate embodiment of the invention, the at least one boundary tag modulates a reflection of the signal transmitted by the mobile transmitter, and this reflected modulated signal is received by the central control station. Then, the central control station would determine if the mobile transmitter has come into the proximity of the boundary tag. In an additional alternative embodiment of the invention, the boundary tag records the receipt of the signal from the mobile transmitter. The central control station then transmits a second signal to the boundary tag. The boundary tag receives the second signal and modulates a reflection of the second signal to produce the reflected modulated signal, which is then received at the central control station.
Optionally, at least one boundary tag may have a unique identifier. The system can then include a processor programmed to determine if the mobile transmitter is in communication with at least one boundary tag whose unique identifier matches at least one predetermined unique identifier. This processor can be located in the central control station, or in the transceiver, or in another location in the system.